This invention relates generally to techniques for processing an organ removed from a donor so as to render it suitable for storage, shipment and eventual transplantation, and more particularly to a system which facilitates a chilling procedure for an organ after it is removed from a donor so that the organ may be maintained in a healthy condition for a relatively prolonged period and shipped in this condition to a transplantation site where a heating procedure is carried out just prior to transplantation.
While the invention shall be described in connection with the processing of kidneys, it is to be understood that similar chilling and heating procedures using essentially the same technique are applicable to other organs such as the liver and the pancreas.
The kidneys are two reddish, bean-shaped organs near the vertebral column at the small of the back, the left kidney lying somewhat higher than the right. The purpose of the kidney is to separate urea and other waste products from the blood. For life to be maintained, at least one kidney must function properly. Blood entering the kidney through the renal artery is returned to circulation in purified form through the renal vein. The waste in the form of urine is excreted by way of the urethra and the bladder.
A kidney is composed of a large number of functional units called nephrons with their associated ducts and blood vessels. A nephron has two parts; namely, the corpuscle which is a bundle of capillaries (glomerulus) enclosed in a capsule, and a tubule which is a long, thin tube leading from the capsule to a collecting tube. Blood flows through the incoming arteriole to the glomerulus, the blood pressure forcing everything in the blood except cells and proteins to filter through the thin walls of the capillaries into the capsule. The remaining blood then flows through the outgoing arteriole to capillaries surrounding the tubule. The resultant filtrate forms at a rate depending on blood pressure and the highly variable rate of blood flow through the glomerulus. The filtrate passes from the capsule into the tubule.
Kidneys are subject to congenital malfunction, physical injury, infections such as Bright's disease, stone formation, arteriosclerosis and tumors. It is for this reason that artificial kidneys are now standard equipment in hospitals where they serve to cleanse and otherwise alter the patient's blood flushed through it. Where a kidney is irreparably affected, it may be replaced surgically by transplantation.
The concern of the present invention is with the processing of a healthy kidney after it has been extracted from a donor and before it is transplanted in a recipient, the kidney during this period being "in limbo".
The present "in limbo" practice, after the kidney is surgically removed from the donor is to flush the organ with a kidney preservative liquid, such as the electrolyte solution 5A7810 marketed by Travenol Laboratories, Inc. of Deerfield, Ill. This solution contains a high concentration of potassium and phosphate and is compatible with blood. The solution, before infusion in the kidney, is chilled in ice to 0.degree.-4.degree. C. (32.degree.-39.2.degree. F.).
The chilled solution is dispensed from a solution bottle held at a height sufficient to produce a continuous gravity flow, the kidney being flushed until the cortex is pale and the effluent is clear, evidencing the disappearance of blood from the kidney. This action is carried out with the kidney in a sterile storage container. After the preservative solution has been perfused, the remainder of the solution is dispensed into the storage container which is then sealed. The storage container housing the flushed organ is then placed within a thermally-insulated shipping carton in which it is surrounded with ice. The ice does not come into direct contact with the organ in the storage container.
A kidney, "in limbo" is subject to rapid biological decay unless steps are taken to maintain it in a healthy state for the period elapsing between its time of removal from the donor and the time of transplantation. With existing techniques, the "in limbo" period must be relatively short and is numbered in hours rather than days. Hence it is not presently possible to transport a kidney extracted from a donor in California to a recipient, say, in London; for the time involved is beyond that which can be tolerated with existing procedures.
And even if transplantation could be arranged to take place within a few hours after the kidney is extracted, conventional preservation and storage techniques do not ensure a healthy organ; hence a significant percentage of transplants involve kidneys which do not function properly in the recipient, possibly because of damage to the kidney during the "in limbo" period. In this regard, reference is make to the article by Lee et al., "Medical Complications of Renal Transplantations" in the Supplement to Urology, June 1977, Vol. IX, No. 6.
To preserve a kidney, it should be maintained in a cold state so that the metabolic needs of the kidney are kept at a minimum. However, one cannot freeze a kidney; for the resultant ice crystals would destroy its cellular structure. Hence to effect preservation, it is essential that the kidney be brought as rapidly as possible to a temperature close to its freezing point without, however, subjecting it to thermal shock, and that the kidney be thereafter maintained at this low temperature until just prior to transplantation, when its temperature must be returned to a level close to body temperature.
In the prior technique, the preservation solution in the gravity-flow infusion bottle is at a temperature of 0.degree. to 4.degree. C., which means that the kidney processed thereby, because of poor heat transfer, will, after flushing, be cooled to a temperature somewhat above 4.degree. C. or 39.2.degree. F. While the flushed kidney in the sterile storage container is thereafter subjected to cooling by ice in the transportation carton, it must be borne in mind that an organ has poor thermal conductivity, and that it takes a significant amount of time for the kidney in the storage container to be adequately chilled by the exterior ice. This time factor may be damaging to the kidney.
Moreover, the flushing procedure which involves continuous gravity flow through the complex network of kidney vessels may not result in effective penetration, for this flow is not analogous to that encountered in vivo. In the human circulatory system, blood is caused to flow as a consequence of the force exerted by the periodic contraction of the heart, which undergoes a regular cyclic contraction (systole) followed by relaxation (diastole). The amount of blood pressure depends on the cardiac output; that is, the volume of blood pumped out of the heart per minute and arterial resistance. The blood vessel network in the kidney is adapted to operate in conjunction with the heart pump; and when preservation fluid is perfused therethrough continuously under gravity pressure rather than under pulsatory pressure in a manner simulating the action of the circulatory system, adequate penetration of the fluid in the kidney may not be realized.
Moreover, in existing techniques the kidney is not stored in its sterile container in a manner isolating it from mechanical shocks, and it may be damaged in handling and transport.